net: openthread: add wake-up end device support

Add Kconfig option to enable the Wake-up End Device role.

Signed-off-by: Eduardo Montoya <eduardo.montoya@nordicsemi.no>
Signed-off-by: Damian Krolik <damian.krolik@nordicsemi.no>
Co-authored-by: Andrzej Kuroś <andrzej.kuros@nordicsemi.no>